The invention relates to an apparatus for and to a method of fixing or polymerizing the binding agent of a dyestuff to a printed web of material by means of heat. The web is introduced into a closed chamber, is subsequently deposited on moving support members and is brought to treatment temperature which, during the stay in the chamber, continues acting on the web. Thereafter, the web of material is discharged from the chamber. A method of this type is mostly carried out such that the web of material is conveyed via a number of support members embodied as guide rollers so as to obtain a large quantity of material per unit of capacity of the closed chamber.
Known methods have the drawback that the web of material is conveyed through the chamber with a certain tension, as a result of which there may occur undesired deformations in the web.